Tony Blair has invested everything - and most certainly his personal credibility - in the hunt for Saddam Hussein's weapons of mass destruction.

Now the Iraq Survey Group has so far found no weapons of mass destruction in Iraq, although has unearthed some evidence of research and development, the prime minister's critics will have a field day.

But as each day has passed, the prime minister's room for manoeuvre has narrowed

The thing that is absolutely certain is that the stakes could not be higher.

Ever since the war ended, the prime minister has insisted he was confident weapons would be found.

And he told his doubters, with increasing irritation, that they should wait until the group reported before leaping to judgements.

Products or programmes?

On at least one occasion Mr Blair suggested he was aware of some of the group's findings.

He didn't say so in as many words, but journalists at one of his monthly news conferences earlier in the summer were left speculating that he must be confident they had found something.

Of course, that something may not have been physical weapons.

The weapons threat was key to Blair and Bush's case for war

Maybe it was "evidence of WMD programmes" or "WMD products" - the phrases the prime minister had started deploying when questioned too hard.

And sure enough, that's what the group says it has found in significant amounts.

But that will not placate his critics. And the prime minister knows that full well.

Unless real weapons are found, the backlash against the war, which is already growing in the wake of the Hutton inquiry, is almost certain to escalate.

Of course the ISG report is not clear cut as all that and it is only an interim report.

Rising scepticism

The group is asking for more time to complete their search - but that is precisely what UN inspector Hans Blix wanted before the war.

But as each day has passed, the prime minister's room for manoeuvre has narrowed.

Anti-war opinion has hardened while scepticism and suspicion have increased.

It may be that a couple of months or so ago, discovery of some evidence that Saddam was developing weapons of mass destruction or had hidden his weapons before the conflict might have been enough.

But the series of inquiries into the war suggesting the threat from Iraq was not as serious as suggested, and the recent comments by Mr Blix that Saddam destroyed his weapons over a decade ago, have added to public distrust.

Mr Blair needs something concrete from the survey group if he is to stand any chance of finally putting this crisis behind him.